Project Summary: Both Type 1 and 2 diabetes result from reductions in pancreatic ?-cell mass and function. Thus, a major goal of the NIH/NIDDK is to develop novel drugs and tools that can lead to replacement and/or regeneration of human ?-cells. This is has proven difficult, because adult human ?-cells are refractory to engagement in cell cycle progression. This project is in response to PAR16-121 to extend the level of early stage pharmacological validation of novel targets, novel chemical scaffolds that are not the focus of significant efforts in the biotechnology and pharmaceutical industry for treatment of diseases within the mission of the NIDDK. The goals of this proposal align well with these objectives and specific areas of interest including medicinal and computational chemistry, structural biology and pharmacological validation of novel targets for diabetes. Specifically, we have recently reported in Nature Medicine in 2015 that a type I DYRK1A kinase inhibitor activates both rat and human ?-cell replication at rates that approach those required for therapeutic human ?-cell replication. This work was published and confirmed by other labs. We envision three components to exploiting these results: A, Optimization of DYRK1A inhibitors for beta cell proliferation since there are NO known compounds of this class in clinical development; B, Tissue Specific Targeting to pancreatic beta cells currently underway in our labs funded by NIDDK grant (R01 DK015015-01-A1); C, Understanding the effects of the immune system on newly replicated beta cell which can only be addressed after successfully completing components A and B. Current known DYRK1A inhibitors target the type I ATP-binding pocket of kinases and have significant liabilities for further drug development. Our premise is that novel leads, developed for the specific use for ? - cell proliferation will provide further validation of this target of interest to NIDDK. Our strategy of kinase optimization coupled with powerful phenotypic assays will lead to improved inhibitors. To that end, we have identified novel drug-like leads that target the inactive kinase (DFG-out type II kinase inhibitors). These results provide the basis for a drug discovery effort that includes a molecular target, in vitro/in vivo ?-cell biology, and viable starting points for medicinal chemistry optimization. In this application, our experienced team of ?-cell biologists, computational and medicinal chemists will pursue three translational Specific Aims: Specific Aim 1. Develop two novel, structurally distinct type II DYRK1A inhibitors with kinase/off-target selectivity and oral bioavailability for ?-cell proliferation using structure-based drug design. Specific Aim 2. Evaluate these novel compounds for inhibition of DYRK1A, ?-cell proliferation and function, optimized kinase and off-target selectivity profiles using biochemical and cell-based assays. Specific Aim 3. Evaluate optimized DYRK1A inhibitors for in vivo ADME PK, efficacy using animal models of reduced ?-cell mass, diabetic animal models and their safety profiles in normal rodents.